The objective of this research is to restore the ability to walk to spinal cord injured (SCI) individuals. Previous studies (by several researchers) have demonstrated that FES can effectively restore legged mobility (with the help of a stability aid), and that such legged mobility can provide significant physiological and psychological benefits to SCI users. Due to the potential of collapse (from muscle fatigue) and the need to guide uncontrolled degrees of freedom, hybrid systems appear to offer the greatest promise for commercially viable gait restoration. As such, recent efforts by various researchers have focused (and are focusing) on the development of hybrid systems. Despite this, a commercially viable hybrid FES system does not yet exist. The intent of this proposal is to develop a commercially feasible gait restoration system, namely one that eliminates the possibility of collapse (due to muscle fatigue), has a low threshold for implementation and use, provides a stable, efficient gait (i.e., a swing-through gait primarily powered by the lower limbs), and is donned and doffed independently and with a minimal level of effort. The proposed system utilizes a hybrid FES approach, which combines two channels of surface stimulation (quadriceps of each leg) with a unique microcomputer-controlled orthosis, called a joint-coupled controlled-brake orthosis (JCO), the combination of which provides a stable, safe, commercially viable gait restoration system for paralyzed persons. Specifically, the use of surface stimulation pro- vides a low threshold of implementation, but at the cost of limited muscular access (i.e., inability to directly access deep hip flexion muscles). This limitation is addressed by the orthosis, which includes a mechanical biasing of the knee joint and unidirectionally couples knee flexion to hip flexion, and with this combination pro- vides the hip and knee flexion required for reliable swing-through gait. The effect of muscle fatigue is greatly diminished by utilizing unique controllable brakes at the hip and knee joints to provide isometric torques (in place of muscle stimulation), and since the knee brakes are normally locked, the risk of collapse is essentially eliminated (even in the event of a power failure). The orthosis provides for smooth, repeatable control of limb trajectories, which is enabled by the combination of joint angle sensors and the proportionally controllable brakes, which are used to guide the limbs (i.e., joint angles) along a desired trajectory. Since the power for gait is provided by metabolic sources, the orthosis requires a minimal amount of on-board power. Finally, the approach is designed to facilitate independent donning and doffing with minimal user effort. As such, the pro- posed system has the characteristics (i.e., fail-safe, low fatigue, moderate exertion, easy don/doff, low electric- al power requirements) of a commercially viable self-contained gait restoration system. If successful, the pro- posed approach could transition in a direct manner to a viable commercial product, and therefore could significantly improve the quality of life of many SCI individuals suffering from complete paralysis of the lower limb. PUBLIC HEALTH RELEVANCE: There are currently about 255,000 spinal cord injured individuals in the United States, with roughly 12,000 new injuries sustained each year, of which approximately 6300 of these (cases per year) result in complete paralysis of the legs with sufficient remaining arm functionality to potentially use the proposed gait restoration approach. Among the significant impairments resulting from paraplegia is the loss of legged mobility. The system proposed herein is intended as a supplement to (and not as a replacement of) a wheelchair, and in particular is intended to provide many of the physiological and psychological benefits of legged mobility that a wheelchair cannot, such as decreased osteoporosis, reduced incidence of decubitus ulcers, improved cardiovascular health, improved bowel and bladder function, reduced spasticity, and increased morale, self-image, and self- esteem.